Risk factors associated with positional plagiocephaly in healthy Iranian infants: a case-control study

Objectives Deformation of the skull by external forces in the absence of synostosis has been defined as positional plagiocephaly (PP). The aim of this investigation was to determine the risk factors of PP in healthy Iranian infants. Materials & Methods This case-control study was performed on 300 healthy Iranian infants aged 8-12 weeks who were referred to the pediatric neurology clinic at Shahid Beheshti Hospital of Kashan. Plagiocephaly evaluations were done using Argenta’s scale. Results Based on multivariate logistic regression analysis, there was a significant association between PP and male gender (OR=2.26; P=0.002), head circumference (OR=1.22; P=0.006), multiple pregnancy (OR=2.55; P=0.03), abnormal presentation in uterine (OR=2.18; P=0.02), primiparity (OR=2.43; P=0.003), and supine sleep position (OR=2.97; P<0.001). However, type of delivery, firmness of headrest, oligohydramnios, and prolonged labor were not correlated with PP. Conclusions The current investigation supports the idea that head circumference, male gender, primiparity, multiple pregnancy, supine sleep position, and abnormal presentation in the uterine are correlated with a greater incidence of PP. Further investigations should be undertaken to understand PP and its related risk factors fully.


Introduction
Deformation of the skull by external forces in the absence of synostosis has been defined as positional plagiocephaly (PP) (1). This condition is of concern because the related changes and deformities, including abnormal head shape, frontal bossing, facial dissymmetry, ear misalignment, and asymmetrical orbits, can be permanent (1).
After the "Back to Sleep" campaign, the incidence rate of sudden infant death syndrome decreased by approximately 50% from 1992 to 2001. However, there was a significant increase in PP, currently a common problem faced by physicians (2). It can be developed in the uterus, during birth, or after birth. The postnatal form of PP is one of the most frequent abnormal findings in otherwise healthy infants (3). Based on prior reports, some of the well-known risk factors for PP in a normal child include supine sleep position, lack of tummy time, bottle propping, and common use of car seats or swings seats (4)(5)(6). Although supine sleep is a major risk factor for plagiocephaly, not all supine sleepers develop PP (7). Furthermore, multiple factors, such as gestational age, intrauterine position, assisted delivery, oligohydramnios, birth order, presentation at birth, gender, ethnicity, infant neck disorders, developmental delay, and different infant care practices, may cause this problem (8).
Even if the prognosis of plagiocephaly is good, the deformities are persistent if not managed as soon as possible, with psychosocial complications (9,10).
Infants with plagiocephaly might be less active than healthy matched controls (2). Some researchers have also indicated a relationship between PP and developmental delay, most frequently in motor functions and language (10). Thus, developmental evaluation is suggested as a part of the treatment of infants with this problem (11). Moreover, if immediately treated, fewer infants will require helmet therapy or physical therapy, decreasing discomforts and losing money and time for the health system (12).
Although there is enough knowledge regarding the risk factors associated with PP in infants with developmental delay or other diseases, less is recognized about why PP occurs in healthy infants.
In the current study, to better understand, we investigated some probable risk factors associated with PP in healthy Iranian infants.

Materials & Methods
The present case-control study was designed to

Statistical analysis
Data were analyzed by the univariate logistic regression method for each risk factor. Odds ratios, P-values, and 95% CIs were calculated for every risk factor. At last, risk factors with a P-value <0.25 in the univariate regression method were analyzed as independent factors in the multivariate logistic regression method. A P-value < 0.05 was considered significant. All analyses were performed using SPSS software version 16 (Chicago, Illinois, USA).

Results
Based on univariate logistic regression analysis,

Discussion
Our finding indicated six factors associated with PP. These factors were male gender, head circumference, multiple pregnancy, abnormal presentation in the uterine, primiparity, and supine sleep position. Oligohydramnios, prolonged labor, firmness of headrest, and delivery type showed significant association with PP.

Factors related to pregnancy
The occurrence of plagiocephaly in multiple pregnancy may be due to an increase in uterine size (14, 15). Another explanation is that multiple pregnancy can lead to greater uterine tension by increasing abnormal presentations risks, such as breech or transverse presentation (16). As we know, multiple pregnancy is also a risk factor for preterm labor, which is a potential risk factor for PP and Gardner et al. (18). Also, premature newborns have less activity and delayed motor function than term neonates, which can induce PP (19,20).
This study confirms that primiparity is associated with a greater risk of PP. In accordance with our results, previous studies have demonstrated a significant association between PP and primiparity (4,19,21). A possible explanation for these results is that the pelvic muscles in primiparous mothers have higher strength than multiparous ones, which limits fetus movements in the uterine (16,(22)(23)(24). We considered cephalic presentation a normal presentation, and other presentations, such as transverse and breech, were considered abnormal presentations. There are several possible explanations for this association. This association may be related to a higher risk of breech presentation in multiple pregnancies, which is a known risk factor for PP (19). Also, some researchers believe that uterine presentation is associated with postnatal head position preferences during sleep (25,26). According to our findings, no significant correlation was found between oligohydramnios and PP. This supports evidence from a study conducted by Oh et al. (27), but our findings are in contrast with those of McKinney et al. (28). Finally, delivery type and prolonged labor were not associated with PP in our study.

Infant factors
Our findings indicated that the male gender was remarkably associated with PP, which is in agreement with prior studies. Male gender is a well-known risk factor for developing PP (4,17,19,21,27,29). This association may be related to greater head circumferences and less flexibility in male newborns (17,(30)(31)(32). Greater head in male fetuses is more vulnerable to deformation during labor (33,34). Another explanation for this is that the male head grows faster after birth, resulting in a higher PP incidence in male neonates (29,35). The current study found that higher head circumference was related to a greater chance of developing PP.

Postnatal factors
We found a significant association between PP is a remarkable cause of unexpected death among infants. However, the notable point is that the prone sleep position is a well-known risk factor for developing SIDS; thus, physicians suggest sleeping in a supine position to prevent SIDS, which can lead to PP (43). Therefore, several recommendations are given by pediatricians to prevent both PP and SIDS, such as changing the head position regularly when putting the infant down to sleep, increasing tummy time, and decreasing the time sating in car seats, cots, and bouncers (21,38,44,45). In this investigation, we found no significant relationship between PP and firmness of headrest, which is in accordance with the findings of Hutchison et al. (38).

Limitations
One of the limitations of this study was the low number of participants. Another limitation was that we did not evaluate other risk factors, such as birth weight, mother's education, parents' occupation, etc. This issue should be considered in the interpretation of our findings.

In Conclusion
The current investigation supports the idea that head circumference, male gender, primiparity, multiple pregnancy, supine sleep position, and abnormal presentation in the uterine are correlated with a greater incidence of PP. These findings extend our knowledge of PP and its related risk factors, which is crucial to identifying infants with a greater risk of PP. Further investigations should be undertaken to understand PP and its related risk factors fully.